The design of distributed data network topologies has been practiced for many years. The need for a comprehensive method for constructing a distributed data communication network results from the complexity of such a system. A distributed data communication network is a hierarchical system of hardware components arranged to connect each hardware device, directly or indirectly, to every other device. At the lowest level in the hierarchy are user terminals or host devices, which form part of the local access network. These terminals are linked to one or more concentrators, which are statistical multiplexers with several low data rate input data lines and fewer high data rate output data lines. The concentrators form the second level of the network hierarchy and, together with the terminals, form the local access network.
The concentrators, which may be connected to other concentrators in a hierarchical fashion, are ultimately connected to the backbone, which forms the highest level in the network hierarchy. The backbone consists of high data capacity lines, or backbone links, that terminate at backbone nodes. A backbone node consists of one or more devices including switching devices for routing traffic within the backbone. Data traffic from the concentrators enters the backbone at the backbone nodes via the switches. A collection of terminals and associated concentrators are aggregated into a cluster and the devices in the cluster all connect to one or more switches at a single backbone node. More than one cluster may be associated with a single backbone node.
The backbone links can be conventional 56 kilo-bit per second data lines or fiber optic T1 lines effectively comprising 24 56 k lines. T1 lines offer lower cost per unit capacity, while multiple 56 k lines offer higher reliability through redundancy than a single T1 line. A well designed backbone will frequently require use of both T1 lines and 56 k lines to achieve required levels of reliability and performance at the lowest possible cost. Some of the existing backbone link configuration methods design backbones based on T1 lines, while others use 56 k lines. None of the existing methods are capable of designing a backbone based on a combination of T1 and 56 k lines. The invention described herein overcomes the deficiencies of the existing methods with a system that permits the configuration of a hybrid backbone incorporating both T1 and 56 k lines as backbone links. The invention also allows the use of three alternative initial network topologies.